Media access control scheme for serially linked devices

• US 7,142,556 B1
• Filed: 12/28/2000
• Issued: 11/28/2006
• Est. Priority Date: 12/28/2000
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Smith, Malcolm M
• Primary Examiner(s): Rao, Seema S.
• Assistant Examiner(s): MOORE JR, MICHAEL J
• Application Number:
  US09/752,844
• Time in Patent Office: 2,161 Days
• Field of Search: 370/382, 370/364, 370/464, 370/465, 370/519, 370/516, 370/461, 370/462, 370/463, 370/229, 370/438, 370/445, 370/447, 370/439, 700/17, 700/83, 709/223, 709/224
• US Class Current: 370/462
• CPC Class Codes: H04L 12/4035 in which slots of a TDMA packet structure are assigned based on a contention resolution carried out at a master unit TDM/TDMA multiplex systems per se H04J3/1694; hybrid switching systems H04L12/64
• CPC Class Codes: H04L 67/125 involving control of end-device applications over a network
• CPC Class Codes: H04L 69/24 Negotiation of communication capabilities

Abstract

A network includes a master station and terminal devices each coupled using a serial data interface to a modem that in turn couples to a twisted pair line. These elements communicate information using a media access control scheme in which a device claims access to the twisted pair line and communicates information on the twisted pair line while the line is claimed. More specifically, a device with information to transmit claims the line by asserting a request to send (RTS) line of its serial data interface, communicates information while the RTS line is asserted, and de-asserts the RTS line upon completing transmission. In addition, the master station and terminal devices implement delays between communications on the line in order to reduce the probability of data collisions.

Claims

1. A communications apparatus comprising:

a serial data interface having a data carrier detect (DCD) line and a request to send (RTS) line each coupled to a modem, wherein the modem couples to a twisted pair line that couples to a plurality of remote devices; and

a processor operable to detect a de-assertion of the DCD line, to assert the RTS line after a period of time from detecting the de-assertion of the DCD line, to communicate information to a selected one of the remote devices while the RTS line is asserted, and to de-assert the RTS line after communicating the information, wherein the period of time comprises a propagation delay for signals transmitted on the twisted pair line and a random period of time after the propagation delay.

2. The apparatus of claim 1, wherein the serial data interface is an RS-232 interface.

3. The apparatus of claim 1, wherein asserting the RTS line requests the modem to generate a carrier signal that causes assertion of DCD lines for the plurality of remote devices coupled to the twisted pair line.

4. The apparatus of claim 1, wherein the selected remote device comprises a master station managing a plurality of components of a supervisory control and data acquisition (SCADA) system using the twisted pair line.

7. The apparatus of claim 1, wherein the propagation delay is a predetermined value.

5. A communications apparatus comprising:

a serial data interface having a data carrier detect (DCD) line and a request to send (RTS) line each coupled to a modem, wherein the modem couples to a twisted pair line that couples to a plurality of remote devices;

a processor operable to detect a de-assertion of the DCD line, to assert the RTS line after a period of time from detecting the de-assertion of the DCD line, to communicate information to a selected one of the remote devices while the RTS line is asserted, and to de-assert the RTS line after communicating the information, wherein the processor is further operable to generate internet protocol (IP) packets encoding the data and to communicate the packets to the selected remote device while the RTS line is asserted; and

a component interface operable to receive data from a component for communication to the selected remote device.

6. A communications apparatus comprising:

a serial data interface having a data carrier detect (DCD) line and a request to send (RTS) line each coupled to a modem, wherein the modem couples to a twisted pair line that couples to a plurality of remote devices;

a processor operable to;

detect a de-assertion of the DCD line;

assert the RTS line after a period of time from detecting the de-assertion of the DCD line;

communicate information to a selected one of the remote devices while the RTS line is asserted; and

de-assert the RTS line after communicating the information, wherein the processor is further operable to;

detect an assertion of the DCD line;

receive a communication from the selected remote device, wherein the communication comprises an address and a command;

determine that the address indicates the component; and

issue the command to the component; and

a component interface operable to receive data from a component for communication to the selected remote device.

8. A method for communicating information over a twisted pair line comprising:

detecting a de-assertion of a data carrier detect (DCD) line for a serial data interface, wherein the serial data interface couples to a modem coupled to the twisted pair line;

after a period of time from detecting the de-assertion of the DCD line, asserting a request to send (RTS) line for the serial data interface, wherein asserting the RTS line requests the modem to generate a carrier signal that causes assertion of DCD lines for a plurality of remote devices coupled to the twisted pair line, and wherein the period of time comprises a propagation delay for signals transmitted on the twisted pair line;

communicating information to a selected one of the remote devices while the RTS line is asserted, wherein the information comprises internet protocol (IP) packets; and

de-asserting the RTS line after communicating the information.

9. The method of claim 8, wherein the serial data interface comprises an RS-232 interface.

11. The method of claim 8, wherein the propagation delay is a predetermined value.

12. The method of claim 8, wherein the period of time further comprises a random period of time after the propagation delay.

10. A method for communicating information over a twisted pair line comprising:

detecting a de-assertion of a data carrier detect (DCD) line for a serial data interface, wherein the serial data interface couples to a modem coupled to the twisted pair line;

after a period of time from detecting the de-assertion of the DCD line, asserting a request to send (RTS) line for the serial data interface, wherein asserting the RTS line requests the modem to generate a carrier signal that causes assertion of DCD lines for a plurality of remote devices coupled to the twisted pair line;

communicating information to a selected one of the remote devices while the RTS line is asserted, wherein the selected remote device comprises a master station managing a plurality of components of a supervisory control and data acquisition (SCADA) system using the twisted pair line;

de-asserting the RTS line after communicating the information;

detecting an assertion of the DCD line;

receiving a communication from the master station, wherein the communication comprises an address and a command;

determining that the address indicates a local component; and

issuing the command to the local component.

13. Logic for communicating information over a twisted pair line, the logic encoded in media and operable to:

detect a de-assertion of a data carrier detect (DCD) line for a serial data interface, wherein the serial data interface couples to a modem coupled to the twisted pair line;

after a period of time from detecting the de-assertion of the DCD line, assert a request to send (RTS) line for the serial data interface, wherein asserting the RTS line requests the modem to generate a carrier signal that causes assertion of DCD lines for a plurality of remote devices coupled to the twisted pair line;

communicate information to a selected one of the remote devices while the RTS line is asserted, wherein the information comprises internet protocol (IP) packets; and

de-assert the RTS line after communicating the information.

14. The logic of claim 13, wherein the serial data interface comprises an RS-232 interface.

15. Logic for communicating information over a twisted pair line, the logic encoded in media and operable to:

detect a de-assertion of a data carrier detect (DCD) line for a serial data interface, wherein the serial data interface couples to a modem coupled to the twisted pair line;

after a period of time from detecting the de-assertion of the DCD line, assert a request to send (RTS) line for the serial data interface, wherein asserting the RTS line requests the modem to generate a carrier signal that causes assertion of DCD lines for a plurality of remote devices coupled to the twisted pair line;

communicate information to a selected one of the remote devices while the RTS line is asserted, wherein the selected remote device comprises a master station managing a plurality of components of a supervisory control and data acquisition (SCADA) system using the twisted pair line;

de-assert the RTS line after communicating the information;

detect an assertion of the DCD line;

receive a communication from the master station, wherein the communication comprises an address and a command;

determine that the address indicates a local component; and

issue the command to the local component.

16. Logic for communicating information over a twisted pair line, the logic encoded in media and operable to:

detect a de-assertion of a data carrier detect (DCD) line for a serial data interface, wherein the serial data interface couples to a modem coupled to the twisted pair line;

after a period of time from detecting the de-assertion of the DCD line, assert a request to send (RTS) line for the serial data interface, wherein asserting the RTS line requests the modem to generate a carrier signal that causes assertion of DCD lines for a plurality of remote devices coupled to the twisted pair line, and wherein the period of time comprises a propagation delay for signals transmitted on the twisted pair line;

communicate information to a selected one of the remote devices while the RTS line is asserted; and

de-assert the RTS line after communicating the information.

17. The logic of claim 16, wherein the propagation delay is a predetermined value.

18. The logic of claim 16, wherein the period of time further comprises a random period of time after the propagation delay.

19. A communications apparatus comprising:

means for detecting a de-assertion of a data carrier detect (DCD) line for a serial data interface, wherein the serial data interface couples to a modem coupled to a twisted pair line;

means for, after a period of time from detecting the de-assertion of the DCD line, asserting a request to send (RTS) line for the serial data interface, wherein asserting the RTS line requests the modem to generate a carrier signal that causes assertion of DCD lines for a plurality of remote devices coupled to the twisted pair line;

means for communicating information to a selected one of the remote devices while the RTS line is asserted;

means for de-asserting the RTS line after communicating the information; and

means for detecting an assertion of the DCD line;

means for receiving a communication from a master station, wherein the communication comprises an address and a command;

means for determining that the address indicates a local component; and

means for issuing the command to the local component.